So.. How else can I think of this?

You're probably asking yourself, and frankly, I'm here to answer it. The better way to think of it is saying, "A positive self affirming attitude draws more self encouragement and improve the way that you look at the situation." It may be wordy, but it captures the essence of the myth. Aside from the original saying (You can do it if you just believe you can!) it is still encouraging a positive attitude but leaves room for minor error. We can all think of a time where we walked out of the classroom saying to ourselves, "Dude, I totally aced that test!" Then we come back the next class period, get that test back, and see a grade much lower than we expected. It's a situation that happens in daily life, and the modern words we would use for the original phrase is probably along the lines of, "Man, I am totally going to OWN this test," or, "I am going to make smoldering mince meat out of this test!" As we see though, it does not always hold true. So in conclusion a positive attitude will boost your positive outlook on a situation, but it does not prevail as the ONLY thing that you need.